Field of the Invention
Embodiments of the present invention relate generally to a charged particle beam writing method, and a charged particle beam writing apparatus, and more specifically relate to a method and an apparatus that perform a proximity effect correction and a resist heating correction, for example.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
FIG. 10 is a conceptual diagram explaining operations of a variable-shaped electron beam writing or “drawing” apparatus. The variable-shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular (rectangular) aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., x direction) during writing. In other words, a quadrangular shape that can pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system.
With the development of the optical lithography technology, and the wavelength reduction (shorter wavelength) due to EUV, the number of electron beam shots required for mask writing is acceleratedly increasing. On the other hand, for ensuring the line width accuracy needed for micropatterning, it has been aimed to reduce shot noise and pattern edge roughness by making resist less sensitive and increasing the dose. Thus, since the number of shots and the amount of dose increase limitlessly, the pattern writing time also increases limitlessly. Therefore, it is now considered/examined to reduce the writing time by increasing the current density.
However, if the substrate is irradiated with an increased amount of irradiation energy as higher density electron beams in a short time, another problem occurs in that the substrate overheats resulting in a phenomenon called “resist heating” of changing the resist sensitivity and degrading the line width accuracy.
On the other hand, in the electron beam writing, when writing a circuit pattern by irradiating a mask, which is coated with resist, with electron beams, a phenomenon called a “proximity effect” occurs due to backscattering of the electron beams penetrating the resist film, reaching the layer thereunder to be reflected, and entering the resist film again. Thereby, a dimensional change (variation) occurs, that is, a written pattern is deviated from a desired dimension. In order to avoid this phenomenon, a proximity effect correction operation that suppresses such dimensional change (variation) by modulating the dose is for example performed in the writing apparatus.
However, even if the dose has been adjusted by the proximity effect correction operation, if subsequently a temperature correction operation is performed for dose modulation in order to suppress dimensional change (variation) due to the resist heating described above, there arises another problem in that a correction residual error occurs in the proximity effect correction. In other words, in performing a resist heating correction, since the dose which is set for obtaining a target dimension after correcting the resist heating is different from the dose which was assumed/estimated at the time of the proximity effect correction, the pattern critical dimension (CD) obtained after the resist heating correction is deviated from the target dimension. In order to cope with this problem, it can be thought to again perform a proximity effect correction calculation, but, it may result in throughput degradation. Further, it will be necessary to newly devise a method for a proximity effect correction calculation to be performed for the second time. For example, there is disclosed a method of calculating a polynomial including a dose modulation coefficient as an element based on a region representative temperature which increases by heat transfer due to irradiation of electron beams, and repeating the calculation until the difference between a value obtained by calculating the polynomial and a dose threshold value becomes within an allowable value (for example, refer to Japanese Patent Application Laid-open No. 2014-209599). Thus, it is desired that a correction residual error can be eliminated even if no second proximity effect correction calculation is performed.